The present invention relates to ion beam devices and, more particularly, to a field ionization source that is specially configured to minimize contamination of an ion beam target.
Liquid metal ion guns are used routinely to generate focused ion beams for analysis of a substrate. Liquid metal ion sources are typically very bright and are well-suited for applications requiring sharp focus of the ion beam and maintenance of a suitable ion fluence. Typically, the ion fluence of a liquid metal ion gun is of the same order as that of a field emission source of a conventional scanning electron microscope. However, liquid metal ion guns typically use gallium, indium, or gold.
The present invention embodies the recognition that gallium, indium, gold, and other conventional materials are not well suited for all ion source applications. For example, where an ion beam is to be used to analyze a semiconductor target, the use of gallium, indium, or gold as a sputter ion source material may lead to unacceptable contamination of the substrate. Accordingly, there is a need for a field ionization source that does not embody the disadvantages of the conventional types of ion sources, particularly in the context of focused ion beam defect analysis systems.
This need is met by the present invention wherein an organic field ionization source is provided and is arranged to be suitable for use in focused ion beam defect analysis systems.
In accordance with one embodiment of the present invention, an organic field ionization source is provided comprising: an ionization needle, an extraction electrode, a voltage source, and a heated reservoir. The ionization needle defines a tip. The extraction electrode defines an extraction aperture therein and is positioned such that the extraction aperture is disposed proximate the tip of the ionization needle. The voltage source is arranged to maintain the tip of the ionization needle at a high potential relative to the extraction electrode. The heated reservoir contains an organic ion source material therein in contact with the ionization needle. The heated reservoir is arranged to maintain a temperature of the organic ion source material at a magnitude sufficient to encourage capillary flow of the organic ion source material from the heated reservoir along the ionization needle to the tip of the needle. The high potential, the extraction electrode, the tip of the ionization needle, and the organic ion source material are selected and arranged such that the organic material is ionized at the tip of the needle and such that organic ions are drawn through the extraction aperture from the tip of the needle.
The organic ion source material preferably comprises coronene, phenylalanine, a vacuum grease, a diffusion pump oil, or another organic material with a boiling point of at least from about 250xc2x0 C. to about 450xc2x0 C.
In accordance with another embodiment of the present invention, a focused ion beam defect analysis system is provided comprising an organic field ionization source, a target, and an electrode assembly. The organic field ionization source comprises an ionization needle, an extraction electrode, a voltage source, and a heated reservoir. The ionization needle defines a tip. The extraction electrode defines an extraction aperture therein and is positioned such that the extraction aperture is disposed proximate the tip of the ionization needle. The voltage source is arranged to maintain the tip of the ionization needle at a high potential relative to the extraction electrode. The heated reservoir contains an organic ion source material therein in contact with the ionization needle and is arranged to maintain a temperature of the organic ion source material at a magnitude sufficient to encourage capillary flow of the organic ion source material from the heated reservoir along the ionization needle to the tip of the needle. The high potential, the extraction electrode, the tip of the ionization needle, and the organic ion source material are selected and arranged such that the organic material is ionized at the tip of the needle and such that organic ions are drawn through the extraction aperture from the tip of the needle. The target is subject to analysis by the organic ions and the electrode assembly is arranged along the path of the ions and is configured to direct the organic ions to the target.
The organic ions may comprise fragments of the organic ion source material and the electrode assembly may include a filter arranged to cause selected ones of the fragments to be directed away from the target. The filter may comprise a Wein filter, a magnetic sector, or a time-of-flight system. The electrode assembly may include an ion accelerating electrode, an ion beam focusing electrode, ion beam scanning electrode, and a ion beam deflecting electrode.
In accordance with yet another embodiment of the present invention, a focused ion beam defect analysis system is provided comprising an organic field ionization source, a target, an electrode assembly, and a particle analyzer. The organic field ionization source is arranged to ionize organic ion source material. The electrode assembly is arranged along the path of the ions and is configured to direct the organic ions to the target. The target is subject to analysis by the organic ions and the particle analyzer is arranged to detect particles ejected from the target in response to the incidence of the organic ions on the target.
Accordingly, it is an object of the present invention to provide a field ionization source that is specially configured to minimize contamination of an ion beam target so as to be suitable for use in focused ion beam defect analysis systems, focused ion beam milling systems, or other types of focused ion beam systems. Other objects of the present invention will be apparent in light of the description of the invention embodied herein.